1. Field of the Invention
The present invention relates generally to wind turbines, and more specifically to a large floating wind turbine without bearings and without a gearbox between the turbine and the generator.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Wind turbines are used to covert wind into electric energy by using the wind to drive a rotor shaft that is connected to a generator for producing electricity. Horizontal axis wind turbines are being used on land and even offshore is shallow and deep water (over 1.80 feet deep) to produce electricity from the wind. A horizontal axis wind turbine is the most popular wind turbine at the time and typically includes three large blades that extend from a rotor hub that is directly connected to the rotor shaft of the turbine. The rotor shaft is connected to a generator through a gear box to step up the rotation from around 29 rpm for the propeller rotor to around 1,200 rpm for the electric generator. All of this is contained within a nacelle structure that encloses the power train and is supported on top of a large tower that longer than the length of the blades.
One major problem with these horizontal axis bladed wind turbines is that the gear box used to step up the rotations for use with the generator does not last very long. The gear box is the main limiting factor for the life of the horizontal axis wind turbine.
Another problem with these horizontal axis wind turbines is that the generator and the gear box must be located at high elevations in the nacelle structure which is on top of the tower. Access to the power train requires getting parts and people up to the top of the tower.
Another major problem with these horizontal axis wind turbines is that the blades must be supported on the rotor shaft by large bearings. Currently, most horizontal axis bladed wind turbines are less than 2.5 MW in power because of the structural limits of securing the long and heavy blades to the rotor hub. Turbines of larger power production have been proposed, such as 5 MW horizontal axis bladed wind turbines. However, the size of the blades is so heavy that the bearings cannot support this load for very long and these turbines wear out very fast. Thus, the smaller wind turbines in the range of 1.5 MW to 2.5 MW are used mostly because they can operate for longer periods of time.
Wind turbines are now being used offshore where the wind speed is greater and more sustainable than on land. However, the offshore wind turbines must be supported in the water and therefore the cost of installing and operating these offshore wind turbines is much greater than the land turbines. The wind offshore is greater in the deep water regions of greater than around 180 feet depths. Offshore wind turbines in the deep waters must be supported on a floating platform that is typically anchored to the ocean floor through three or more cables. A regular land wind turbine is secured onto the floating platform to supply the power to drive the generator. Again, as in the land wind turbine limitations, because of the bearings and the generator, these offshore wind turbines are typically limited to the 1.5 MW or 2.5 MW sizes.
One large wind turbine, which of U.S. Pat. No. 6,294,844 issued to Lagerwey on Sep. 9, 2001 shows a floating platform such as a barge or ship that supports a structure, the structure supporting a plurality of wind airfoils. The Lagerwey invention does not use a large wind airfoil, but makes use of a number of smaller airfoils. And additional embodiment shown in FIGS. 15A and 15B shows a vertical wind turbine rotatably supported by a floating ship. In this embodiment, bearings are used to support the rotating turbine, and therefore the size and weight of the rotating turbine is limited.
Another type of floating wind turbine is disclosed in U.S. Pat. No. 3,988,592 issued to Porter on Oct. 26, 1976, and discloses a floating sphere anchored to a sea bed, the sphere carrying a vertical axis wind turbine. The turbine is small and supported for rotation by bearings. As in the above mentioned Lagerwey invention, the invention of Porter is limited as to the size of the wind turbine because of the use of the bearings for rotational support.
Some prior art inventions make use of a floating turbine in which the turbine is located within the water. U.S. Pat. No. 6,734,576 issued to Pacheco on May 11, 2004 discloses in one embodiment a floating generator in which the rotary structure is completely submerged within the water flow path. The structure is supported by a floating barge.
U.S. Pat. No. 7,397,144 issued to the two applicants of the present invention on Jul. 8, 2008 and entitled BEARING-LESS FLOATING WIND TURBINE shows a floating wind turbine with a very large base diameter in order to make the floating wind turbine stable in the water. The barge is ring torus in shape yin order to reduce the viscous drag from the barge rotating within the water. However, the barge requires a large surface area of contact in the water for stability.
There is a need in the art for a larger rotation device that can capture a large amount of wind to generate a large amount of electric power. There is also a need in the art of offshore wind turbines to eliminate the need for a gear box to drive the electric generator. There is also a need to eliminate the use of bearings to support the large rotor lades. There is also a need to eliminate the use of a tower that supports the power train of the wind turbine.